Processes currently being developed for the commercial preparation of ethylene glycol produce a significant quantity of propylene glycol, a by-product with potential value. Since both compounds have similar boiling points and chemical properties, separation of ethylene glycol from mixtures containing propylene glycol by conventional techniques is energy-intensive and expensive. Improved separation processes are of significant interest to the chemical industry.
The following are representative of references which disclose adsorptive separation processes. D. B. Broughton et al., Chemical Engineering Progress, Vol. 66, No. 9pp 70-75 (1970) describe a method of recovering p-xylene from its mixtures with other C.sub.8 -hydrocarbons by adsorption from a liquid phase. Separation is accomplished by making use of small differences in affinity of an adsorbent for various species in the mixture. The p-xylene is recovered from the adsorbent by displacing it with a desorbing liquid which is separated from product streams by fractionation.
A. J. deRosset et al., Ind. Eng. Chem., Process Des. Dev., Vol. 15, No. 2, pp 261-266 (1976) describe use of liquid column chromatography as a predictive tool for continuous countercurrent adsorptive separations. The reference discloses the separation of p-xylene, ethylbenzene, cymene, and p-diisopropylbenzene from mixtures using a "pulse test" procedure. The procedure comprises injecting a sample into a solvent stream flowing through a packed column and detecting species emerging from the column as a function of time, or volume of solvent passed.
U.S. Pat. No. 4,319,058, issued to Kulprathipanja et al., discloses a process for the separation of ethanol from water. The process comprises contacting a feed mixture comprising ethanol and water with an adsorbent comprising a shaped replication of particle aggregates comprising carbonaceous pyropolymers containing recurring units of at least carbon and hydrogen atoms at a temperature in the range of from about 20.degree. to about 230.degree. C. and a pressure in the range of from about atmospheric to about 500 psig. Substantially all of the ethanol is adsorbed to the substantial exclusion of water. High purity ethanol is recovered by passing a desorbing material over the adsorbent.
U.S. Pat. No. 4,349,668, issued to Neuzil et al., discloses a process for separating glucose from fructose by selective adsorption. The process comprises contacting a mixture comprising glucose and frutose with an adsorbent comprising an X zeolite containing potassium cations at the exchangeable cationic sites thereby selectively adsorbing glucose from the feed mixture and thereafter recovering the glucose. Preferably, the glucose is recovered by desorption from the adsorbent with a desorbent material.
U.S. Pat. No. 4,394,178, issued to Chao et al., discloses a process for separating lactulose from admixtures with lactose by selective adsorption. The process comprises contacting a mixture comprising lactulose and lactose at a temperature of from about 30.degree. C. to 100.degree. C. and at a pressure sufficient to maintain the system in the liquid phase with an adsorbent composition comprising specific cationic forms (particularly barium or potassium) of modified zeolite Y, whereby lactulose is selectively adsorbed thereon. The non-adsorbed portion of the mixture is removed from contact with the zeolite adsorbent. The lactulose is then removed by contacting the adsorbent with a desorbing agent.